The present embodiments provide toners, and in particular, emulsion aggregation (EA) toners. These toners exhibit a low melt temperature while simultaneously exhibiting excellent relative humidity sensitivity regarding charging properties. Also described are methods of making such toners.
Advantages of the toners described herein include, for example, the ability to incorporate crystalline materials into the toner to achieve low melting characteristics without sacrificing relative humidity sensitivity.
Low melting, including ultra low melting, toners are known. For example, such toners may be comprised of an amorphous polyester material having a crystalline polyester material mixed therein. The crystalline polyester material imparts the low melting temperature to the polyester toner. An example of such a low melting polyester toner is described in, for example, U.S. Pat. No. 6,830,860 and U.S. Pat. Publication No. 2008/0153027, the disclosures of which are incorporated herein by reference in their entirety.
Polyester toners have been prepared utilizing amorphous and crystalline polyester resins. The incorporation of these polyester resins into toner requires that the resins first be formulated into emulsions prepared by solvent containing batch processes, for example solvent-based phase inversion emulsification (PIE) is known in the art. Ammonium hydroxide (NH4OH) is known in the artas a “basic neutralization agent” in the polyester emulsification process. See, e.g., U.S. Pat. No. 8,192,913. The ammonium hydroxide inverts the resin dissolved oil phase (resin/solvent solution) in water to form a stable aqueous emulsion.
In the PIE process, the type of base or neutralizing agent and ratio of neutralizing agent to resin or solvent plays a very critical role. There are many input process parameters such as resin composition, resin molecular weight and acid value that can vary which make it impossible to emulsify high molecular weight branched amorphous polyester resins to produce the desired particle size range (e.g., 100-250 nm) and a narrow particle size distribution. Lot-to-lot variations of resin acid value, viscosity, and resin softening point requires adjustments in the PIE process parameters such as neutralization ratio and solvent ratio to achieve the desired toner particle size. Determining such adjustments is time-consuming and requires much trial and error to identify the exact conditions that will allow a resin lot to be successfully emulsified. Moreover, even with these modifications some polyester resins are not successfully emulsified, with failed batches where particle size was greater than 400 nm. In particular, certain high molecular weight branched amorphous polyester resins with lower acid values are not emulsified when ammonia hydroxide is used as the neutralization agent.
Therefore, there is a need to identify a new neutralization agent for the preparation of polyester latexes suitable for polymers possessing a variation in parameters such as lower acid value, higher softening point and the like.